12 Answers

You need so much more coverage on this. Octillery has a jaw-droppingly large movepool, so abuse that!

Octozooka's crap. The irony of it all is that this accuracy-reducing move, only has 85 accuracy. Octozooka's mediocre, so surf's up, dudes! (lame pun, I know. xD)

Ice beam is great, and if you had Charge Beam on it, you'd have a makeshift BoltBeam combo, which gives fair coverage against every known type combination that is currently in the game (except for Shedinja). The passive Special Attack bonus is a major plus. Replace Signal Beam for Charge Beam.

Energy Ball is no longer needed, seeing as ground and Rock types are handled by Surf, and Charge Beam has Water covered. You could replace Energy Ball with something strong like Flamethrower to hit Steel, Bug, Grass, and Ice-types.

This gives coverage against ANY Pokemon in Pokemon HeartGold & Soulsilver. If it has a weakness, then chances are, Octillery can handle it. Psychic, Ghost, Dark, and Fighting are the only that are not covered, but you r attacks and raw stats are good enough to deal with them in no time.

Octillery has equally high attack and special attack, so you can’t really go wrong with these stats. Here's a very good special set (the one I'm using). Also, I noticed how many people teach him octazooka that may lower the target’s accuracy. However I personally think that this move isn’t a good choice at all because of low base power, and Octillery has decent defense anyway, so a few hits on him don’t hurt a lot.

Ability-Sniper

Item-Razor Claw (awesome with ability)

Nature-Modest (+Satk- Atk)

Hydro Pump-STAB, powerful (NOT WATER SPOUT BECAUSE OF LOW SPEED!)

Ice Beam (or maybe Blizzard)-Takes out grass weakness and dragons

Mud Slap-Deals with electric weakness

Here, you can put any move you want. I would recommend Energy Ball, Flamethrower (or Fire Blast), or Sludge Wave.

Well hyper beam isn't that good. It is powerful but the rest turn is a no brainer switch and the opposing Pokemon can set up and possibly sweep your team. Also what is the point of soak if you can't hit water types super effectively?

-Surf (pretty self-explanatory)
-Ice Beam (High powered Sp.Attk and to help with type coverages and disadvantages)
-Flamethrower (1. Cause it's awesome that he can learn it and 2. helps his grass type disadvantage and makes him even better against steel)
-Psybeam (helps with fighting types and can confuse which is always good)

I also usually attach a charcoal. The 20% boost you get for fire moves to go along with his high Sp.Attk allows him to blast steel and grass away with no issues and it's better for fending off any electric Pokemon rather than surf or ice beam.

As mentioned before, Octillery has a massive Special Attack movepool, along with a high Sp. Atk stat. It can learn special moves from almost all types (it can learn Flamethrower, Sludge Bomb and Energy Ball while being a monotype). The only flaw to it is its fairly low Speed stat, and its mediocre defensive stats.

Moveset:
-Water SPOUT (not to be confused with Water SPORT). I'm surprised that this wasn't mentioned already. It is an extremely powerful move that very few can learn. It also hits everything on your opponent's side of the battlefield, so it's less riskier than Surf, however if you lose a good fraction og your HP, this move's power decreases pretty badly.

-If you have Sniper and Scope Lens, you might want to try using Focus Energy, but it could potentially waste a turn to give your opponent the advantage over Octillery's defense stats. Octillery likely won't faint on the first hit, but it can definitely happen.

Adding on to this, if you purposely give Octillery low Speed stats, you could easily make a great Trick Room sweeper out of it; you just need something else to use Trick Room before it. I would highly not suggest sending Octillery out first for this reason.

Also, as for the ability Moody, (it boosts any random stat - including evasion and accuracy - by 2, and decreases another stat by 1 at the end of each turn), I would suggest it if possible, as it practically gives you freebie stat boosts without wasting a turn (but it can lower the stats you need too, but not as often). However, due to the fact that it boosts evasion, it is banned on most online metagames, such as Pokèmon Showdown or Pokémon Online. If that's what you're using, I'd suggest Sniper as an ability. But if you are playing competitively on the official Nintendo games, the ability is not banned.